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Lung cancer is the leading cause of cancer mortality worldwide and KRAS is the most commonly mutated gene in lung adenocarcinoma (LUAD). The 78-kDa glucose-regulated protein GRP78/BiP is a key endoplasmic reticulum (ER) chaperone protein and a major pro-survival effector of the unfolded protein response (UPR). Analysis of the Cancer Genome Altas (TCGA) database and immunostain of patient tissues revealed that compared to normal lung, GRP78 expression is generally elevated in human lung cancers, including tumors bearing the KRAS(G12D) mutation. To test the requirement of GRP78 in human lung oncogenesis, we generated mouse models containing floxed Grp78 and Kras Lox-Stop-Lox G12D (Kras(LSL-G12D)) alleles. Simultaneous activation of the Kras(G12D) allele and knockout of the Grp78 alleles were achieved in the whole lung or selectively in lung alveolar epithelial type 2 cells known to be precursors for adenomas which progress to LUAD. Here we report that GRP78 haploinsufficiency is sufficient to suppress Kras(G12D)-mediated lung tumor progression and prolong survival. Furthermore, GRP78 knockdown in human lung cancer cell line A427 (Kras(G12D/+)) leads to activation of UPR and apoptotic markers and loss of cell viability. Our studies provide evidence that targeting GRP78 represents a novel therapeutic approach to suppress mutant KRAS-mediated lung tumorigenesis.

In many cancers, combination therapy regimens are successfully improving response and survival rates, but the challenges of toxicity remain. GRP78, the master regulator of the unfolded protein response, is emerging as a target that is upregulated in tumors, specifically following treatment, and one that impacts tumor cell survival and disease recurrence. Here, we show IT-139, an antitumor small molecule inhibitor, suppresses induction of GRP78 from different types of endoplasmic reticulum (ER) stress in a variety of cancer cell lines, including those that have acquired therapeutic resistance, but not in the non-cancer cells being tested. We further determined that IT-139 treatment exacerbates ER stress while at the same time suppresses GRP78 induction at the transcriptional level. Our studies revealed a differential effect of IT-139 on chaperone protein family expression at multiple levels in different cancer cell lines. In xenograft studies, IT-139 decreased BRAF inhibitor upregulation of GRP78 expression in the tumor, while having minimal effect on GRP78 expression in the adjacent normal cells. The preferential decrease in GRP78 levels in tumor cells over normal cells, supported by the manageable safety profile seen in the Phase 1 clinical trial, reinforce the value IT-139 brings to combination therapies as it continues its clinical development.

Metaplasia is emerging as a key process in tumorigenesis. We discovered that 2 essential endoplasmic reticulum (ER) chaperones, 78-kilodalton glucose-regulated protein (GRP78) and 94-kilodalton glucose-regulated protein (GRP94) have a role in metaplasia. Grp78 haploinsufficiency in the mouse pancreas impairs acinar-to-ductal metaplasia, whereas in the uterus, Grp94 loss induces squamous cell metaplasia; both resulting in tumor suppression.

The 78 kDa glucose-regulated protein (GRP78), also referred to as BiP/HSPA5, is a major endoplasmic reticulum (ER) chaperone with antiapoptotic properties and also serves as a regulator of ER stress signaling (1). Tumor cells are subjected to ER stress due to intrinsic factors such as genetic mutations, altered metabolism and hyperproliferation, as well as extrinsic factors in the tumor microenvironment including oxygen and nutrient deprivation (2). As an adaptive measure, cancer cells turn on the unfolded protein response (UPR), and ER stress induction of GRP78 in cancer cells represents a major prosurvival response, suppressing apoptosis while promoting proliferation and invasiveness. Thus, GRP78 is an emerging target for therapy to blunt cancer development, progression, and drug resistance. GRP78 conditional knockout mouse models further established the requirement of GRP78 in solid and blood tumorigenesis driven by mutation of the tumor suppressor gene PTEN and that GRP78 is an upstream regulator of the PI3K/AKT/S6 pathway (3,4). KRAS is commonly mutated in various cancers, including pancreatic adenocarcinoma (PDAC) and lung cancer, and thus far is deemed “undruggable”. We discovered that haploinsufficiency of a single moiety, GRP78, while having no effect on the normal pancreas, is sufficient to impede acinar-to-ductal metaplasia, block oncogenic signaling, curb PDAC progression, and prolong survival. Similarly, Grp78 haploinsufficiency is able to suppress mutant KRAS-driven lung cancer development. Further, we recently established that ER stress can actively promote cell surface localization of GRP78, where it assumes novel co-receptor functions with cell surface protein partners in regulating signal transduction pathways (5). Our studies uncover that csGRP78 interacts with specific cell surface signaling partner proteins and through those interactions impacts cancer cell adhesion, polarity, migration, and survival. References 1. Lee AS. Glucose-regulated proteins in cancer: molecular mechanisms and therapeutic potential. Nat Rev Cancer 2014;14:263-76. 2. Luo B, Lee AS. The critical roles of endoplasmic reticulum chaperones and unfolded protein response in tumorigenesis and anticancer therapies. Oncogene 2013;32:805-18. 3. Fu Y, Wey S, Wang M, Ye R, Liao CP, Roy-Burman P, et al. Pten null prostate tumorigenesis and AKT activation are blocked by targeted knockout of ER chaperone GRP78/BiP in prostate epithelium. Proc Natl Acad Sci USA 2008;105:19444-9. 4. Wey S, Luo B, Tseng CC, Ni M, Zhou H, Fu Y, et al. Inducible knockout of GRP78/BiP in the hematopoietic system suppresses Pten-null leukemogenesis and AKT oncogenic signaling. Blood 2012;119:817-25. 5. Tsai YL, Zhang Y, Tseng CC, Stanciauskas R, Pinaud F, Lee AS. Characterization and mechanism of stress-induced translocation of 78-kilodalton glucose-regulated protein (GRP78) to the cell surface. J Biol Chem 2015;290:8049-64. Citation Format: Amy S. Lee, Jieli Shen, Daisy Rangel, Chun-Chih Tseng, Yuan Li Tsai, Dat P. Ha, He Zhao, Louis Dubeau. GRP78/BiP: Cancer's comrade in crime [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr SY13-03. doi:10.1158/1538-7445.AM2017-SY13-03